Regenerative propellant guns wherein a liquid propellant is pumped into a combustion chamber and ignited so as to propel a projectile from the barrel of the gun are known. Such contemporary regenerative liquid propellant guns typically comprise a variable volume combustion chamber wherein inner and outer concentric pistons cooperate to pump and meter additional liquid propellant into the combustion chamber as the combustion process proceeds. Liquid propellant disposed within a reservoir formed between the inner and outer pistons is forced out of the reservoir as the inner and outer pistons are moved in a combustion chamber volume increasing direction as a result of the combustion process.
The liquid propellant is forced through an annular opening formed between the inner and outer pistons as the inner and outer pistons travel in the combustion chamber volume increasing direction. The flow of liquid propellant from the reservoir is metered into the combustion chamber by the annular orifice whose area depends upon the relative positions of the inner and outer pistons.
The ignition of liquid propellant within contemporary regenerative liquid propellant guns is typically performed as a four step process. In the first step, a mail box or primer charge is ignited at the distal end of an ignition tube connected to the combustion chamber. In the second step, the primer charge ignites a larger intermediate quantity of liquid explosive disposed within the tube at a position closer to the combustion chamber. In the third step, the intermediate charge ignites a puddle charge disposed within the combustion chamber. In the fourth step, the puddle charge ignites the main charge so as to initiate regenerative combustion of liquid propellant sprayed from the reservoir into the combustion chamber of the gun. As such, the initiation of the main charge involves an undesirably complex and unreliable series of separate steps.
Prior to ignition of the puddle charge disposed within the combustion chamber, the inner and outer pistons are in a minimum combustion chamber volume position wherein the inner and outer pistons cooperate to close the annular orifice defined therebetween and thus prevent the flow of liquid propellant from the reservoir into the combustion chamber.
Upon ignition of the puddle charge, increased pressure within the combustion chamber urges the inner and outer pistons in a combustion chamber volume increasing direction. Typically, the inner piston, having a greater surface area than the outer piston, is urged in the combustion chamber volume increasing direction at a slightly faster rate than the outer piston. Thus, such relative motion of the inner and outer pistons causes them to separate and open the annular orifice to the liquid petroleum reservoir. Movement of the inner and outer pistons reduces the volume of the liquid propellant reservoir, thus forcing liquid propellant from the liquid propellant reservoir into the combustion chamber at a rate determined by the movement of the inner and outer pistons and the area of the annular orifice formed therebetween. Such pumping of the liquid propellant from the reservoir into the combustion chamber by the inner and outer pistons facilitates the regenerative combustion process so as to accelerate a projectile through the barrel of the gun.
Such regenerative guns commonly utilize a liquid propellant comprising a concentrated aqueous nitrate salt solution. Such concentrated aqueous nitrate salt solutions are substantially viscous and dense. They require an elevated temperature and pressure in order to sustain continuity in the combustion reaction.
The aqueous nitrate salt solutions commonly utilized in regenerative propellant gun applications typically comprise hydroxylammonium nitrate (HAN) and triethanolammonium nitrate (TEAN). It has been suggested that combustion of the HAN and TEAN involves a first reaction wherein the decomposition of HAN releases hydroxyl radicals and heat so as to produce an increase in pressure within the combustion chamber, followed by a subsequent reaction involving the rapid chemical reaction of the TEAN.
The ignition of such premixed fuel/oxidant liquid propellants is commonly initiated in contemporary regenerative propellant guns by electrical arcs, explosives and lasers, for example, which provide the conditions necessary to sustain completion of the subsequent chemical reactions. However, the heat initially generated by such contemporary ignitors is rapidly absorbed by the water component of the aqueous nitrate salt solution, thus generating steam. A substantial quantity of the energy provided by such contemporary ignitors is thus undesirably utilized in converting the water of the aqueous nitrate salt solution into steam, thereby increasing the quantity of energy which must be provided by the ignitor in order to heat and ignite the liquid propellant.
The puddle charge utilized in contemporary regenerative guns inherently has a limited surface area available for atomization and reaction, further increasing the quantity of energy required to be provided by the ignitor. Such puddle charges of liquid propellant inherently result in slow and very directional combustion reactions.
Because the energy requirements for reliable ignition of the liquid propellant in contemporary regenerative propellant guns is substantial, the use of electrical energy, i.e., electrical arcs, lasers, etc., is not convenient for battlefield applications.
Furthermore, it is difficult to attain reliable and consistent ignition of liquid propellants in such contemporary regenerative propellant guns. Reliability and consistency of ignition of the liquid propellants used in contemporary regenerative propellant guns is reduced due to the high energy requirement for such ignition and the low surface area associated with the puddle charge used therein.
Such inconsistency in the ignition process is thought to contribute to the generation of undesirable combustion oscillations which occur as additional liquid propellant is sprayed into the combustion chamber during the regenerative process. Such combustion chamber oscillations inhibit precise control of the combustion process which is required for accurate operation of the regenerative propellant gun. As such, it is desirable to provide a means for attaining reliable and consistent ignition of liquid propellants in regenerative propellant guns so as to mitigate the occurrence of undesirable combustion chamber oscillations.
Furthermore, the above-mentioned difficulties in initiating combustion of such liquid propellants present an additional concern regarding the safe disposal of contaminated, excess, or waste liquid propellant. The disposal of such contaminated, excess, or waste liquid propellant causes substantial environmental concern.
Thus, an alternative method for igniting liquid propellant which is safe, controlled, simple, and reliable is desirable from a military, as well as an environmental point of view.